1. Field of the Invention
The present invention relates to a method for manufacturing an electronic component, and more particularly, relates to a method for manufacturing an electronic component, such as a triaxial acceleration sensor, which includes a mechanically operable functional unit and requires a space that allows displacement or vibration of the functional unit and also requires an airtight seal.
2. Description of the Related Art
A technique of interest to the present invention is described in, for example, Japanese Unexamined Patent Publication No. 2002-231920, which discloses a solid-state image sensing device provided on a solid-state image sensor chip, with an airtight sealing unit formed of a flat plate of a transparent member and a frame unit formed on the undersurface of the flat plate. In the solid-state image sensing device, the frame unit is made of a chip-side polyimide film formed by printing in a region of the solid-state image sensor chip except at least a light receiving unit and a flat plate-side polyimide film formed by printing in a region of the flat plate corresponding to the chip-side polyimide film, and the chip side polyimide film and the flat plate side polyimide film are joined to each other with an adhesive interposed therebetween.
However, when an adhesive is used to join the two polyimide films in accordance with the method described in Japanese Unexamined Patent Publication No. 2002-231920, it is difficult to repeatedly apply the same predetermined amount of adhesive so as to provide a uniform thickness, thereby leading to a problem in that the thickness of the frame unit after the joining process, that is, a gap between the solid-state image sensor chip and the flat plate unit, is varied due to variations in the thickness of the applied adhesive and variations in loading in the case of joining by heating after the application. It is to be noted that this problem is not particularly elicited in the solid-state image sensing device disclosed in Japanese Unexamined Patent Publication No. 2002-231920.
On the other hand, electronic components such as, for example, triaxial acceleration sensors or surface acoustic wave filters as MEMS (Micro Electro Mechanical Systems) components include a mechanically operable functional unit, and require the securing of a space which allows displacement or vibration of the functional unit and require airtight sealing. When the method using an adhesive as described in Japanese Unexamined Patent Publication No. 2002-231920 is applied to a method for manufacturing an electronic component such as a triaxial acceleration sensor, the problem which is not elicited in the solid-state image sensing device will be elicited below.
A triaxial acceleration sensor which has a typical structure includes a substrate with a sealing frame formed on a periphery of one main surface and with a mechanically operable functional unit arranged in a region surrounded by the sealing frame, and a cover with a sealing layer formed over the entire surface of the one main surface, the sealing layer to be joined to the sealing frame, and the substrate and the cover are integrated by joining the sealing frame and the sealing layer to each other. Then, this integration of the substrate and cover results in securing of the space between the substrate and the cover which allows displacement or vibration of the functional unit, and also results in an airtight seal.
In the case of the triaxial acceleration sensor, the functional unit includes a spindle unit, a beam unit for supporting the spindle unit in a displaceable manner with respect to the substrate, and a piezoresistive unit for detecting a stress caused in the beam unit.
In such a triaxial acceleration sensor, the gap between the substrate and the cover restricts the displacement magnitude of the spindle. Thus, when the gap between the substrate and the cover is varied due to variations in the thickness of the applied adhesive and variations in loading in the case of joining by heating as described above, the variations in acceleration detection performance and durability will be caused. Furthermore, when an insufficient amount of adhesive is applied, the joining strength will be decreased. On the other hand, when an excess amount of adhesive is applied, the extra adhesive will flow out between the sealing frame and the sealing layer to adhere to the functional unit, thereby leading to a problem that the acceleration detection performance is degraded or varied.